The present invention relates to pressure-responsive systems and components. Specifically this invention relates to devices and systems that sense the level or depth of fluids and responds thereto by triggering switching mechanisms.
It is often desirable to know information about fluid levels in tanks. Determining fluid levels and controlling fluid levels in tanks, such as in sewage tanks, water cisterns or tanks, and other fluid system and storage vessels, whether enclosed or open and exposed to the environment, has been done in a number of ways. For example, in tanks that are visually accessible, an operator may periodically take visual readings of the fluid level.
Visual readings, however, are often not desirable, in systems where an automatic response is required when the fluid level reaches a certain threshold. In such cases the activation of a pump or valve may be necessary to move more fluid into the vessel or to discharge fluid from the vessel. In systems where visual readings are not available or when an immediate response is required, control systems are typically employed that are responsive to a fluid level indication. Such control systems may illuminate a light on an indicator panel representing the fluid level and/or trip an alarm to notify a human operator that corrective action is required.
Unfortunately having a human operator manually initiate a corrective function may not be desirable due to the repetitive nature of the function or due to the inefficiency of having a human operator in the system. As a result, control and indicator functions are typically handled by electronic control systems which are responsive to one or more switches that are triggered by fluid level or pressure input. For example, in sewage tanks it is well known to use multiple tilt style float switches to control the fluid level. These may be mercury switches or rolling ball switches, where a ball triggers a microswitch within the mechanism. These switches are triggered when the whole switch mechanism tilts downward toward a tethered connection a sufficient amount. Tilt style float switches are typically attached via an anchor tether either directly to the vessel interior wall, or to a bar, rail, or other vertically disposed structural member within the vessel. A plurality of these tilt style float switches are often disposed vertically with each one representing a unique elevation of fluid level within the vessel.
Unfortunately, numerous problems have been encountered with these mechanisms. For example, turbulent conditions within a fluid-holding vessel can negatively impact performance of float switch systems. Such turbulence is often the result of fluidized material inflow and/or pump-discharged fluid material exiting the tank. This turbulence can create undesirable eddies and waves within the tank that can cause tethered tilt style float switches to become entangled, thus preventing them and the system from proper operation. In addition, the turbulence within the tank can cause inadvertent switching and what is often referred to as xe2x80x9ccontact chatterxe2x80x9d of the switches within the tilt style float switch assemblies. Inadvertent switching can cause system inefficiency and degradation, such as a false level reading which causes a pump to turn on or off earlier or later than desired. Such contact chatter can cause the pump, which is responsive to the triggered switch, to cycle inadvertently on and off at a high rate, resulting in undue and undesirable system wear and operation. Consequently there exists a need for a fluid level sensing and control system which is more reliable in turbulent environments.
Other problems that can result from tilt style float switches include the fact that they are disposed adjacent the surface of the fluid material in the sewage tank. Such environments are often highly corrosive and greasy. These tethered switches can become damaged from banging against each other and the tank wall during the turbulent system operation. In addition, the greasy outer surface of the tilt style float switches can cause them to intermittently adhere and even get stuck against the tank wall, thus affecting system performance and reliability. In addition, low pressure sewage system tanks in both residential and commercial use are often of corrugated side wall construction. These corrugations can serve as a series of mini-ledges or shelves to the grease-covered tilt style float switches, thus facilitating their adherence and entrapment. The tilt style float switches can also become corroded. Leaking mercury from some styles of these switches poses a serious environmental and health hazard. Non-mercury versions of the tilt style float switches can similarly be ruined by corrosion of their contact or leads, thus rendering them inoperable. Consequently there exists a need for a fluid level sensing and control system which is more reliable in corrosive, greasy, and/or contaminated environments.
Another type of known switching mechanism performs similarly to the typical toilet, in which a ball floats with the fluid level and closes the valve when the tank is full after the toilet is flushed. In these switching mechanisms, the ball floats on the liquid and bumps switches on and off. As with tilt style float switch assemblies, ball float switching mechanisms can only represent the actual liquid level when the switch is bumped and triggered. Consequently there exists a need for a fluid level sensing and control system which can indicate a range of fluid levels. There also exists a need for a fluid level sensing and control system which can be easily adjusted to change the range of fluid levels being monitored.
Another common problem with all of the aforementioned tilt style float switches, and vertical ball float switches is in servicing these systems. Since they are disposed in sewage tanks or other fluid vessels, servicing them can be a messy, less than ideal, undertaking. Consequently there further exists a need for a fluid level sensing and control system which is easier to service.
It is an object of the exemplary form of the present invention to provide a fluid level sensing and control system.
It is a further object of the exemplary form of the present invention to provide a fluid level sensing and control system which accurately and reliably indicates fluid levels within a reservoir.
It is a further object of the exemplary form of the present invention to provide a fluid level sensing and control system which accurately and reliably indicates fluid levels within reservoirs with turbulent environments.
It is a further object of the exemplary form of the present invention to provide a fluid level sensing and control system which is operative to reliably indicate fluid levels for reservoirs with corrosive, greasy, and/or contaminated environments.
It is a further object of the exemplary form of the present invention to provide a fluid level sensing and control system which is operative to control the input and/or output of fluids within a reservoir responsive to the fluid level in the reservoir.
It is a further object of the exemplary form of the present invention to provide a fluid level sensing and control system which is easy to configure and service.
It is a further object of the exemplary form of the present invention to provide a fluid level sensing and control system which does not require electrical components disposed within the fluid of the tank.
Further objects of exemplary forms of the present invention will be made apparent in the following Best Modes for Carrying Out Invention and the appended claims.
The foregoing objects are accomplished in an exemplary embodiment of the invention by a pressure activated control apparatus that includes a first resilient member having a first or outer surface exposed to the fluid and is responsive to the fluid pressure to trigger one or more switches of a force translation and switching mechanism. The pressure activated control apparatus includes a second or inner surface exposed to the inside of the apparatus that is sealed from the fluid. The force translation and switching mechanism responds to changes in the force exerted by the pressure of the fluid on the outer surface of the first resilient member to trigger one or more switches. The pressure activated control includes a second resilient member that provides a biasing force against the force translation and switching mechanism in a direction opposite to the force exerted by the fluid pressure on the outer surface of the first resilient member. In this way, change in height of the fluid level within the vessel compared to movement of the force translation and switching mechanism is greater than one-to-one.
The apparatus of the exemplary form of the present invention provides a reliable, affordable alternative to known tilt style float switches, vertical float switching assemblies and electronic pressure transducer-based systems used for, among other possibilities, determining fluid level or controlling fluid level in open or enclosed fluid holding vessels, such as fluid storage or septic tanks, cisterns, sump and sewage basins, and other fluid system and storage vessels. In one embodiment, the pressure activated control of the present invention is provided in an elongate, vertically disposed housing that can be connected to an interior side wall of a tank, cistern or other fluid-holding vessel, such that the first resilient member has an outer surface that is substantially always in contact with the fluid. The first resilient member can be a pliable rolling diaphragm made of durable nitrite rubber, or any other suitable material selected based on the environment it is to be exposed to, including chemical and thermal environments. In one exemplary embodiment, the rolling diaphragm is in the shape of a bellofram, or a cup with a radially outwardly extending peripheral flange at its upper open end (i.e., it is top hat-shaped), that is sealed at its flange to the housing near a first or lower housing end. The rolling diaphragm acts together with a push cup, a rod and a plunger that are centrally disposed in the elongate housing to serve as a substantially zero friction piston to actuate or trip one or more switches, such as a plurality of microswitches.
In one exemplary embodiment, the second resilient member may be a spring of a selected spring constant, xe2x80x9ck,xe2x80x9d that is disposed within the housing between the push cup and an annularly disposed spring plate which is connected to the housing. The spring can be annularly disposed around the rod and provides a biasing force against the push cup and rolling diaphragm, such that for every linear distance of movement of the piston assembly, which includes the rolling diaphragm, push cup, rod and plunger, vertically upward within the housing, a multiple greater than one times that lineal distance of incremental fluid level is being represented by that piston assembly movement. Simply changing the spring to one with a different spring constant k, allows for a different fluid level range to be sensed or controlled with the same pressure control apparatus. For example, one spring can give approximately eighteen inches of fluid level representation or control with about four inches of corresponding piston assembly travel, whereas a second spring can give forty-two inches of fluid level representation or control. Consequently, substituting a different spring (different k constant) will give a correspondingly different range of fluid level control.
In one exemplary embodiment of the present invention, a plurality of microswitches are housed in a head portion of the housing, at a second or upper housing end. The microswitches are each adjustably and removably connected on a switch track assembly such that each one is tripped at a different plunger vertical elevation within the housing, thereby allowing for adjustable fluid level control within the vessel.
In one exemplary embodiment, the switch track assembly comprises a top piece and a bottom piece connected by four identical spaced switch mounting rails, or switch track rods. The microswitches are each connected to a switch coupler piece that snaps onto an adjacent pair of the rods, such that the switch trigger can be contacted by the plunger coming through a hole in the bottom piece of the switch track assembly in response to sensed fluid pressure on the overall piston assembly. Each switch coupler and corresponding microswitch pair can easily be snapped along the switch track rails making for an adjustable fluid level control system. In an alternative embodiment, the switch track assembly can accommodate up to fourteen such commercially available microswitches each mounted on a removable switch coupler to two adjacent switch track rods.
Although one surface of the rolling diaphragm is meant to be continuously exposed to fluid material in the tank at a subsurface fluid level, the remaining interior of the housing is sealed from the fluid and can be connected to a source of fresh air, such as by a vent tube or line connected at some upper apparatus location to outside air external to the fluid vessel. In this way, the switches are not exposed to corrosive liquids or gases within the vessel and the volume of air displaced by the rolling diaphragm and piston assembly in response to a fluid elevation increase in the vessel can be vented. Correspondingly, the vent line serves as a source of fresh air brought into the apparatus when the fluid elevation within the vessel is decreased, such as by a pump discharge cycle, and the rolling diaphragm unrolls or relaxes with the piston assembly moving downward.
In exemplary embodiments of the present invention, the housing may be made substantially from a combination of commercially available, off-the-shelf standard sized PVC piping, couplers, reducers, aluminum bar stack, and the like, and from a minimum number of specially fabricated components (such as of molded ABS, Lexan(copyright) (General Electric Company) or other suitable plastic, or fabricated from another suitable material), thereby minimizing system cost. In one exemplary embodiment, four microswitches can be provided representing, from lowest to highest elevation along a switch track assembly: off, pump on one, pump on two, and an alarm, respectively. Such an arrangement is common in preexisting sewage tank systems, thereby making for easy retrofit of tilt style float switch sewage tank systems with the present invention. The present invention can simply replace the tilt style float switches and be wired to the existing control system. Servicing the system and adjusting the switches and corresponding fluid control levels can be done simply and in the field, without any tools. In another exemplary embodiment for sensing fluid level and indicating the same, fourteen microswitches can be provided. Such a system could be employed to represent a series of fluid elevations on an indicator panel and have an alarm level, e.g. Of course in other exemplary embodiments longer piston assemblies and switch track assemblies could be substituted allowing for more microswitches and more range of fluid level representation and control.
The pressure activated control apparatus and system of exemplary forms of the present invention provide a reliable, affordable and easily serviceable means to trigger a switching apparatus in response to fluid pressure or level. No electric cords or components are submerged in the fluid. The fluid level can be adjustably controlled by the apparatus. The apparatus operates within its own enclosure envelope and senses fluid pressure at a subsurface fluid level, such that it is not susceptible to turbulent surface conditions or the greasy surface layer typically found in sewage tanks that is known to affect system performance and reliability.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments. For example alternative exemplary embodiments of the present invention may include a control device that is responsive to pressure changes of gases caused by the displacement of a diaphragm of an exemplary embodiment of a pressure responsive device. Such a control device may include manually adjustable switches for selecting a desired depth range for the liquid in a reservoir. Current depth levels may be visually displayed by the described exemplary embodiment of the control device in terms of a percentage of the selected depth range for the liquid. In addition, switches, pumps, valves and alarms may be triggered when the determined depth level of the liquid breaches one or more selectable thresholds. Such thresholds may be represented by the controller as a percentage of the selected depth range for the liquid.